Obj. 2.01

1
Obj. 2.01
2
The Atom History Recap

• Democritus The indivisible atom
• Matter is composed of empty space through which
  the atoms move
• The differing properties of matter are due to the
  different sizes, shapes and movement of the atoms.

Solid, homogeneous, indestructible and
indivisible (400 BC)

• Changes in matter are due to changes in the
  arrangements of the atoms and not from changes in
  the atoms themselves.

(atomos uncuttable)
Obj. 2.01
3
Daltons atomic theory particulate nature of
matter
(1803)

• Indivisible atom
• All atoms of an element are identical (same size,
  mass and properties) and unique (not like any
  other elements atoms)
• Atoms combine in simple whole number ratios to
  form compounds.
• Chemical reactions cause atoms to be separated,
  combined or rearranged.

2 H2
1 O2
2 H2O
Obj. 2.01
4
J.J. Thomson The plum pudding model

• 1897-Discovered the electron and proved that the
  atom was NOT indivisible (consisted of smaller
  particles)
• 1904-Proposes that the atom consisted of two
  partsa large positively charged mass with
  electron raisins mixed in with it.

Obj. 2.01
5
Ernest Rutherford gold-foil experiment (1911)
Hypothesis If Thomsons model of the atom is
valid, then a positive particle will be able to
pass through an atom with little deflection.
Experiment Bombard thin gold foil with alpha
particles (nuclei of helium atoms) and measure
the amount of deflection.
Obj. 2.01
6
(No Transcript)
7
Obj. 2.01
8
Ernest Rutherford gold-foil experiment (1911)

• Most of the atom consisted of empty space.
• All of the positive charge and virtually all of
  the atoms mass is contained in a dense region
  in the center called the nucleus.
• The electrons move rapidly through empty space
  outside of the nucleus.

• 1920-Rutherford refines model the nucleus
  contains positively charged particles called
  protons (1 charge).
• 1932-Third subatomic particle, the neutron (0
  charge) discovered by James Chadwick.

Obj. 2.01
9
Niels Bohr planetary model of the atom (1913)
Obj. 2.01
10
(No Transcript)
11
Schrödinger Electron cloud model (1926)

• In the quantum mechanical model of atomic
  structure, electrons do not travel along fixed
  paths like planets around the sun.
• Instead, electrons can be found most frequently
  in certain areas around the nucleus.

Obj. 2.01
12
(No Transcript)
13
Homework tonight Writing Assignment 2
14
Quantum mechanical model 90 probability of
finding electron within 3D orbital with a maximum
energy defined by the principal quantum number,
n. (n the row number on the periodic table)
Obj. 2.01
15
n 3 9 sublevels 18
electrons
3s 2 e-
3p 6 e-
3d orbitals 10 e-
Obj. 2.01
16
Atomic number number of protons
protons electrons IN NEUTRAL ATOMS
Obj. 2.02
17
So, how are the electrons arranged around the
nucleus?
Obj. 2.02
18
The electrons in an atom have different energies
depending upon how close to the nucleus they are.
The energy levels are spaced apart like steps on
a flight of stairs.
32 e-
electrons 2n2
18 e-
Level 4
8 e-
Level 3
Level 2
2 e-
Level 1
Energy
nucleus
Obj. 2.02
19
Lets build some atoms!
AKA
Bohr Rings Aren't Boring!!
Obj. 2.02
20
In neutral atoms, p e
Hydrogen
-1
0 n
1 p 0 n
Atomic number the number of protons in the
nucleus
Mass number the number of protons the number
of neutrons in the nucleus
Obj. 2.02
21
Helium-4
2 p 2 n
Obj. 2.02
22
Lithium-7
3 p 4 n
Obj. 2.02